Cylinder blocks and other components of marine engines are commonly formed of aluminum alloys because of their high strength-to-weight ratio and corrosion resistance. It would be desirable to fabricate marine engines or engine components of titanium because of the high mechanical properties of titanium and its corrosion resistance. However, titanium is considerably more expensive than aluminum alloys due to difficulties in extracting titanium from its ore. In addition, commercially available titanium contains small residual amounts of oxygen which cannot be removed by conventional extraction processes. Because of this, the use of titanium for marine engines and engine components has not been commercially feasible.
Processes are known for refining pure iron by direct current arc heating. In processes of this type, as described in U.S. Pat. No. 3,203,883, iron containing impurities, such as sulfur and oxygen, is melted in a crucible, and a slag layer, composed of calcium silicate and containing an alkali metal, alkaline earth metal, iron, or aluminum compound, is disposed on the upper surface of the molten iron and heated to a molten state. After the slag has been melted, a D.C. voltage is applied between an anode that is suspended above the slag layer and the cathodic molten metal and the slag then acts as an electron transfer layer, so that impurities, such as sulfur and oxygen, are carried into the slag and oxidized at the upper face of the slag layer to sulfur dioxide and oxygen that is evolved from the melt. At the temperatures involved, the major portion of the oxides of the slag, such as calcium oxide, and are not reduced or effected by the arc heating.